Object detection system having an image detection system

ABSTRACT

An object detection system has an image detection system with an imaging detector, a position detection system with a position detector, and optics which guide incident radiation onto both detectors. The two detectors are arranged one behind the other, in particular adjacent to one another, in the beam path. This makes it possible to achieve a simple, compact and reliable object detection system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of German patent application DE 10 2008 046 362.0, filed Sep. 9, 2008; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to an object detection system having an image detection system with an imaging detector, a position detection system having a position detector and optics which guide incident radiation onto both detectors.

Various optical systems for the detection of a target and for keeping it in view are known for guiding unmanned missiles in the direction of a target. In the case of a passive guidance system, the target can be selected by an operator before the missile is launched, and a reference image of the target scene, with the marked target, can be passed to the missile. During target approach, the target is detected by the missile on the basis of the reference image, which is highly up-to-date because its age is only a few seconds, and the missile can steer itself autonomously to the target.

In the case of a semi-active laser guidance system, the target selected by an operator is illuminated with a marking laser, and a position detection system in the missile detects the angle offset of the illuminated spot relative to its field of view by imaging the radiation reflected from the illuminated spot onto the position detector. The extent of the angle offset is in this case determined by the position or the orientation of the imaged illuminated spot on the radiation-sensitive surface of the position detector. The missile is steered in the direction of the illuminated spot as a function of the determined angle offset, and is thus guided to the target. In this case, the target illumination must be maintained until the missile reaches the target. The target can be illuminated by an observer in an advanced position. Pulsed radiation and pulse repetition rates of about 10-20 Hz are typically used for illumination, with the pulse repetition rate being used to code the laser designator, in order to make is possible to approach the correct target even when there are a plurality of illuminated targets in the seeker field of view. The pulse code of the target illuminator is transmitted to the missile before launch. By way of example, one position detection system is disclosed in commonly assigned German published patent application DE 10 2004 029 343 A1 and its counterpart U.S. Pat. No. 7,304,283 B2.

In order to reduce the danger to an illuminator, for example an observer in an advanced position, it is known for the target to be illuminated for only a short time, for example one second, and for the target to be assigned to the missile in this way. The missile has the characteristic, in the sense of a dual-mode system, of using an imaging system to identify targets which have been marked with a laser target illuminator. The missile can be guided passively to the target with the aid of the image detection system once the target has been transferred by the target illumination and the position detection or, to be more precise, the angle offset of the missile with respect to the target has been determined by means of the position detection system in the missile.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an object detection system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which specifies such a system by means of which an object can be reliably detected as a target and can be tracked in a target scene, so as to allow a missile to be reliably steered to the target.

With the foregoing and other objects in view there is provided, in accordance with the invention, an object detection system, comprising:

an image detection system with an imaging detector;

a position detection system with a position detector; and

optics disposed to guide incident radiation along a beam path onto said imaging detector and onto said position detector;

wherein said imaging detector and said position detector are disposed one behind another in the beam path. In particular, the two detectors are disposed adjoining one another.

In other words, the objects of the invention are achieved by an object detection system of the type mentioned initially in which the two detectors are arranged one behind the other, in particular adjacent to one another, in the beam path. The beam path is therefore first of all guided to one of the detectors, and the same beam path is then guided to the other detector. Arranging the detectors one behind the other makes it possible to save valuable physical space, and the optics can be used not only for the imaging detector but also for the position detector, thus making it possible to achieve a system of little complexity, and of compact design.

The two detectors are expediently arranged adjacent to one another, for example immediately adjoining one another, or separated from one another only by a layer, for example an adhesive layer or an optically active layer, such as a filter.

The detectors are advantageously mounted such that they cannot move with respect to a missile housing.

The imaging detector is preferably mounted on the cooling unit of a cooler, in order to increase its sensitivity. By way of example, the cooler may be a cold finger. It is feasible, of course, to also provide a cooling capability for the position detector.

With a clever design, the optics have an optical element which not only images the beam path on the imaging detector but also guides it to the position detector. The optical element therefore guides the same beam path both onto the imaging detector and onto the position detector. Radiation which is guided onto the position detector can therefore also be guided onto the imaging detector. It is expedient to arrange the last beam-forming or beam-deflecting optical element in the beam path in front of the detectors, and this may be a lens, a mirror, a prism or planar optics. The beam path which is imaged on the imaging detector is expediently completely guided to the position detector. The beam path can be imaged on the imaging detector by arranging the imaging detector on an image plane in the beam path.

The object detection system may be a component of a seeker head of a missile. The image detection system is used to detect an image on which an object which may be marked as a target is imaged. The imaging detector may be a point detector, a line detector or a matrix detector. In the case of a point detector or line detector, the image which reproduces the object can be recorded sequentially by scanning and can be assembled to form the complete image. The position detection system is used to detect a position or to determine an angle offset of the object relative to a coordinate system which, for example, is firmly linked to a missile axis. The position detector can thus be designed such that it outputs angle coordinates which correspond to the offset angle of the target being aimed at, relative to the fixed coordinate system. The angle offset may be detected once, a plurality of times, or continuously. For example, the optics can be carried by the object, corresponding to the position, and a line of sight spin rate can be detected, which is used to steer the missile. Alternatively, in the case of optics which are arranged in a fixed position in the missile, the missile can be steered on the basis of the position itself, with the position being maintained on the missile axis, for example by appropriately steering the missile.

Radiation for which the imaging detector is sensitive can advantageously pass through the position detector. The two detectors may be arranged one behind the other in the beam path, without the rear detector being shadowed. Transmissibility is achieved with a transmission level of at least 50%, in particular at least 80%.

In a further advantageous embodiment of the invention, the two detectors are arranged on the image plane of the beam path. Both the object and the illumination spot can be imaged in focus on both detectors. In this context, the image plane is understood as being a plane with a thickness at right angles to the optical axis of the beam path which is no greater than 10% of the focal length of the beam path on the image plane, in particular 3%.

In order to produce the position detection system, a lateral effect detector is advantageous, which is expediently arranged rigidly in front of the imaging detector. A lateral effect detector may have a very compact design and may be designed to be transmissive for medium infrared and far infrared, which means that an imaging detector which operates in these wavelength ranges can be arranged behind the lateral effect detector, without shadowing. High-purity silicon is advantageous as a detector substrate for the position detector. Furthermore, a lateral effect detector can be made very large, for example up to (20 mm)², as a result of which its field of view covers a wide angle range. A wide field of view can be used for reliable target detection since a large angle scatter can occur in the case of an indirect launch with a ballistic flight path in the direction of the target.

A further advantage of lateral effect detectors, detectors with a transmissively radiation-sensitive surface, is that they can be operated without cooling, and dispensing with a cooling capability makes it possible to save both the costs required for this purpose and physical space.

The two detectors advantageously cover fields of view of different size. While the field of view of the position detector is advantageously large, for example with a diameter of at least 5°, and preferably of at least 15°, the field of view of the imaging detector can be kept small, that is to say for example less than 5° or even less than 1°, since the alignment of the narrow field of view with the target can be carried out by the position detector. The narrow field of view makes it possible to achieve high angle resolution of the imaging detector.

It is, of course, also feasible to design the fields of view of the two detectors to be the same size. This offers the advantage that increased functionality can be achieved. For example, if only an image of inadequate quality can be obtained using the imaging detector, the position of the target with respect to the missile can be determined once again using the position detector. This therefore provides a mutual monitoring capability between the two detectors. The result which one of the detectors produces can therefore be checked by the result which the other detector produces. This allows the missile to be guided particularly reliably to the target.

The field of view of the imaging detector is expediently located in the field of view, in particular centered in the field of view, of the position detector. A simple optics geometry can be achieved by arranging the imaging detector centered with respect to the position detector.

It is also proposed that the position detector be mounted rigidly on a housing of the imaging detector. There is no need for additional holding elements, and the system can be designed to be compact.

A high degree of compactness is likewise achieved if the position detector forms an inlet window of the imaging detector. This can be coated with a spectral filter, expediently on the side facing away from the imaging detector, in order to filter the radiation to the imaging detector.

Irrespective of its position, the spectral filter is expediently designed such that it has a transmission window in the wavelength range of the position detector, a transmission window in the wavelength range of the imaging detector, and an opaque area between the two transmission windows. A single spectral filter can be used for both detectors, thus allowing the object detection system to be kept compact.

If the two detectors are each connected to their own cooling unit, with the cooling units being arranged in one another, then the object detection system can likewise be designed to be compact and simple.

For exact detection of the position of the target being aimed at, it is advantageous for detector outputs of the position detector to be connected to amplifier electronics via a coupling capacitor in order to suppress background radiation, thus resulting in a bias T circuit.

The detector outputs of the position detector preferably have a DC bias voltage applied to them, in order to increase the speed of the detector and thus to widen the bandwidth. If the already mentioned coupling capacitor is in this case arranged downstream from the DC bias voltage supply, then it can not only ensure suppression of background radiation but also outputting of the DC bias voltage and/or AC coupling.

When approaching the target—with the target being illuminated uniformly at the same time—the irradiation intensity (which is detected by the position detector) of the positioning emitter becomes stronger. In order to avoid reaching the saturation range of the position detector, it is advantageous for the object detection system to have an amplifier for signals from the position detector, which amplifier is designed for variable gain matching.

In addition, the object detection system advantageously comprises a control means for controlling the position detection and, expediently, the image processing of the image detection system.

If the control means has a memory in which a position calibration of the position detector is stored, then this makes it possible to ensure that little mechanical adjustment effort is required for the positioning system by means of an electronic calibration.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in an object detection system having an image detection system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. The drawing and the description relate to numerous features in combination, which a person skilled in the art will expediently also consider individually and will combine them to make further worthwhile combinations.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a schematic illustration of an object detection system with Cassegrain optics and with two detectors, attached to one another, on the image plane of the optics; and

FIG. 2 shows a schematic circuit illustration of a position detector.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a seeker head 2 in the front part of a missile 4 with a viewing window 6 in the form of a dome, behind which an object detection system 8 is arranged. The system 8 contains optics 10 in the form of Cassegrain optics with two mirrors 12, 14, by means of which radiation from an object scene 16 with a target 18 is imaged in one beam path 20 onto a detector system 22. The detector system 22 comprises a position detector 24, also referred to as a positioning detector 24, and an imaging detector 26, which is arranged in the beam path 20 immediately behind the position detector 24. The mirror 14 is an optical element which not only guides the beam path 20 onto the imaging detector 26 but also guides the same beam path and/or the same radiation onto the detector 24, for example radiation in the far infrared, which passes through the detector 24 and is guided onto the detector 26.

The object detection system 8 comprises a gyro system on air bearings with a gyro 28 which is monitored by a control means 30, which is also used as evaluation electronics for the two detectors 24, 26. The gyro 28 is connected to the optics 10, which image the incident target radiation onto the large-area position detector 24 and the considerably smaller imaging detector 26. Optics 10 pass the radiation to the two detectors 24, 26 and therefore, because of the different detector sizes, cover two different fields of view. The imaging detector 26 is seated on a cold finger 32 and has only a smaller field of view. The larger position detector 24 is connected to a housing 34 of the imaging detector 26, which is passed around the cold finger 32. The two detectors 24, 26 are mounted rigidly relative to the housing of the missile 4, via the housing 34.

The imaging detector 26 is in the form of a line detector, whose individual images are assembled in a scanning mode to form the overall image of the object scene 16. The metallic housing 34 is used for mounting the position detector 24. The position detector 24 is sensitive in the near infrared spectral range, and detects laser radiation from a target marker which emits in the near infrared, and derives from this the angle offset of the target being aimed at.

The position detector 24 is a lateral effect detector. The infrared light which falls on its active area generates a photocurrent which flows away in the direction of the p-doped and n-doped regions. In contrast to a simple photodiode, the detector 24 has a plurality of electrical contacts, however. This leads to splitting of the photocurrent at the electrodes, which are arranged at the side, as a function of the position of the light spot. The position in the x and y directions can be determined by forming the current difference between two opposite electrodes. Normalization of the total current makes the position signal independent of the incident light intensity.

The viewing window 6, which is in the form of a dome and acts as a protection apparatus against external influences, may be used as the first optical element, for example as a lens, for imaging the object scene 16 onto the two detectors 24, 26. It is composed of a material which has good transmission both for the near infrared and for the medium and far infrared, and which at the same time is very strong. For example, zinc-sulphide Cleartran®, a water-free form of zinc sulphide with a relatively broad transmission range from 0.5 to 14 μm, is very highly suitable for the spectral range from the near infrared to the far infrared.

A spectral bandpass filter 38 is fitted to the position detector 24, to be precise on its side facing the mirror 14, in order to suppress background radiation and for interference suppression. The filter 38 is opaque in the near infrared wavelength range, except for the specific wavelength range of the marking laser, which can pass through the filter. Medium infrared and long-wave infrared can pass through the filter.

FIG. 2 shows a schematic circuit diagram of the lateral effect detector 24 and amplifier electronics connected to it. The detector 24 comprises four signal outputs 42, which are each connected to reading electronics 40, only one of which is illustrated in FIG. 2, for the sake of clarity. The reading electronics 40 are likewise connected to the control means 30, which are also provided for target guidance and thus for steering the missile 4. The irradiation of light onto a spot 44 on the detector 24 initiates a signal at each of the signal outputs 42. The strength of the respective signal depends on the intensity of the light irradiated onto the spot 44 and the position of the spot 44 within the area 46 of the detector 24. The closer the spot 44 is to one of the signal outputs 42, the stronger is the signal at this signal output 42, and the weaker the signal is at the opposite signal output 42. If the spot 44 is positioned precisely at the center point of the area 46, the four signals are all equally strong.

Because of the use of the continuous light-sensitive area 46, the detector 24 can easily be calibrated electronically. The control means 30 have a memory in which a position calibration of the position detector 24 is stored. This position calibration includes the discrepancy between the optical axis and the position on the area 46 at which all four signals are the same.

The reading electronics 40 comprise in each case a bias-voltage source 48, with the bias-voltage sources 48 having a positive bias voltage applied from two opposite signal outputs 42, for example of +15 V, and with the bias voltage sources 48 of the two other signal outputs 42 having a corresponding negative voltage applied, corresponding to the p-doping and n-doping. In order to decouple the bias voltage from the amplifier electronics 50, each of the reading electronics devices 40 has a coupling capacitor 52. The pulses from the marking laser result in an alternating current at the signal outputs 42, as a result of which the coupling capacitor 52 does not lead to any signal interruption. This alternating-current coupling of the detector 24 to the amplifier electronics 50 is used to reduce the background component, and to output the DC bias voltage. A controllable resistor 56 is connected across an amplifier element 54, thus making it possible to vary the signal gain, controlled by the control means 30. The signal can thus be reduced as the missile approaches the target, thus making it possible to avoid overdriving of the detector 24 and of the amplifier electronics 50.

The currents from the signal outputs 42 are supplied via the reading electronics 40 to signal processing electronics which, for example, may be arranged in the control means 30 or between the control means 30 and the reading electronics 40. These signal processing electronics digitize the signals and process them as a function of the functional phase, that is to say as a function of whether the signal is intended to be found as such with the aid of the transfer code, or whether the aim is to find offset angles, by means of a specific algorithm. For a digital interface, these status or offset signals are passed to the autopilot. A further electrical interface is used for the operating voltage supply.

The object detection system 8 may be operated as follows. In an initialization phase, all the hardware and software functions of the detectors 24, 26 and of the electronics are activated by the control means 30 and are switched to the basic state. In addition, the frequency code with which the target is being illuminated by the marking laser is passed to the control means 30. The initialization phase may be initiated, for example, by a launch.

In a subsequent first acquisition phase, the control means 30 in conjunction with the position detector 24 and with the aid of the code search for the marking laser light. For this purpose, all pulses which exceed a threshold value are detected. A pulse sequence of three to six pulses is required for reliable synchronization, depending on the algorithm.

In the subsequent first tracking phase, the current offset angles produced by the detector 24—for example in the form of two mutually perpendicular vectors—are determined precisely with respect to a coordinate system that is fixed to the seeker head, and are used for slaving the gyro system. For example, the optics 10 can be guided in the direction of the identified target on the basis of the offset angle, with the gyro 28 identifying the movement of the optics 10 and the control means 30 aligning the missile 4 in the direction of the target 18, on the basis of corresponding control-surface signals.

If the optics 10—or in the case of rigid optics 10, the missile 4—are or is at least essentially aligned with the target 18, the second acquisition phase starts, in which the imaging detector 26 identifies the target 18. For this purpose, the instantaneous offset angles are transferred to the infrared image of the detector 26, with target marking thus being carried out, thus uniquely defining the target 18. In the second, subsequent tracking phase, the offset angles of the target 18 are determined by means of image processing algorithms by the control means 30, for slaving of the optics 10, from which angles the gyro 28 is used to determine a line of sight spin rate, which is used to guide the missile 4. This phase may continue until the target 18 is reached.

After the second acquisition phase, that is to say after identification of the target 18 by the image processing, the missile 4 can be guided to the target 18 both with the aid of the imaging detector 26 and the imaging processing and—when the target is being marked—solely by the position detector 24 and the corresponding reading electronics 40. The approach phase can therefore be carried out both using the semi-active laser system and using the imaging system. In consequence, the target guidance is particularly insensitive to disturbances. Alternatively, after the image processing acquisition phase, the marking of the target 18 by the marking laser can be ended, and the missile 8 can be guided to the target 18 solely with the aid of the imaging detector 26 and the image processing. 

1. An object detection system, comprising: an image detection system with an imaging detector; a position detection system with a position detector; and optics disposed to guide incident radiation along a beam path onto said imaging detector and onto said position detector; wherein said imaging detector and said position detector are disposed one behind another in the beam path.
 2. The object detection system according to claim 1, wherein said imaging detector and said position detector are disposed directly adjoining one another.
 3. The object detection system according to claim 1, wherein said imaging detector and said position detector are disposed adjacent one another.
 4. The object detection system according to claim 1, wherein said position detector is configured to allow radiation, for which said imaging detector is sensitive, to pass through said position detector.
 5. The object detection system according to claim 1, wherein said imaging detector and said position detector are arranged on an image plane of the beam path.
 6. The object detection system according to claim 1, wherein said position detector is a lateral effect detector.
 7. The object detection system according to claim 1, wherein said imaging detector and said position detector cover fields of view of mutually different sizes.
 8. The object detection system according to claim 1, wherein the two detectors cover fields of view of a common size.
 9. The object detection system according to claim 1, wherein a field of view of said imaging detector is located in a field of view of said position detector.
 10. The object detection system according to claim 9, wherein the field of view of said imaging detector is centered in the field of view of said position detector.
 11. The object detection system according to claim 1, wherein said imaging detector is disposed centrally with respect to said position detector.
 12. The object detection system according to claim 1, wherein said position detector is mounted rigidly on a housing of said imaging detector.
 13. The object detection system according to claim 1, wherein said position detector forms an inlet window of said imaging detector.
 14. The object detection system according to claim 1, which further comprises a spectral filter having a transmission window in a wavelength range of said position detector, a transmission window in a wavelength range of said imaging detector, and an opaque area between said transmission windows.
 15. The object detection system according to claim 1, which comprises a cooling unit connected to said position detector and a cooling unit connected to said imaging detector, and wherein said cooling units for said detectors are disposed within one another.
 16. The object detection system according to claim 1, wherein said position detector has detector outputs connected to amplifier electronics via a coupling capacitor, in order to suppress background radiation.
 17. The object detection system according to claim 1, which comprises an amplifier for signals received from said position detector, said amplifier being designed for variable gain matching.
 18. The object detection system according to claim 1, which comprises a control device having a memory with a position calibration of said position detector stored therein. 